On 16 heinä, 14:38, Sithembewena Lloyd Dube <zebr...@gmail.com> wrote:
> Hi everyone,
>
> I have a queryset of categories and would like to exclude categories with
> no items associated. I am cycling through the queryset as follows, without
> the desired result:
>
> for cat in categories:
> if cat.item_set.count() == 0:
> categories.exclude(pk=cat.pk)
Querysets are always cloned on calling a method, so the right syntax
is:
categories = categories.exclude(pk=cat.pk).
For efficiency reasons you might want to collect all the pks into a
list, and then after the loop do one:
categories = categories.exclude(pk__in=pk_list)
The queryset cloning can be expensive if you do a lot of operations.
Of course, the annotation way given downthread is likely to be the
most effective way to do this.
- Anssi
--
You received this message because you are subscribed to the Google Groups
"Django users" group.
To post to this group, send email to django-users@googlegroups.com.
To unsubscribe from this group, send email to
django-users+unsubscr...@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/django-users?hl=en.
